I need to connect PVC to this old sewer pipe:
This is the pipe that came off:
I temporarily capped it with a 3 inch fernco and a rubber mallet. Can I permanently use a 3 inch to 2 inch fernco?
Plumbing – How to connect PVC to this non-threaded metal sewer pipe
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Long Term Update: I did use one of these "expanding" repair flanges and it was fine. It's been over two years since the repair with no issues!
Toilet Flange OATEY Mfr #: 43539
If you notice at the top, there is a handy dandy nut (if you will) that you can unscrew. Take that off, and you're half way to removing it.
After that, you can unscrew the bottom of the p trap from the rest of the pipe.
Next you will need a PVC P trap kit. Make sure you bring your old pipe to the hardware store and check that you get the correct size (Most kitchen sinks are 1 1/2 or 1 1/4 in.)
Figure out the correct orientation of your p trap. The long pipe included should fit inside of the existing metal pipe nicely. If not, shorten it a little bit with a hack saw. Careful though, the pvc is fragile and easy to crack!
You should be able to save the original section of pipe you unscrewed first if you disconnect it from the sink. (See red arrow) The PVC part of the p trap should screw nicely into the green arrow part of the pipe. You may need to use the original nut, but if that doesn't fit, use the pvc one included in the kit. Make sure it's tight!
Have fun!
Best Answer
You are looking at an attempt to attach a plain steel drain pipe to a cast iron hub-and-spigot drain pipe. The hub-and-spigot technology is obsolescent or obsolete. It was labor-intensive, quite robust, and suitable to the materials available in the nineteenth century.
You can buy hubs and spigots suitable for connecting modern materials such as PVC to existing hub-and-spigot plumbing. If you go this route you can expect to make one more labor-intensive caulked joint, and switch the rest of your pipes to modern types upstream of that joint.
You can also use a donut to connect modern plumbing to a hub. I consider this less robust but if you can fasten down the involved pipes so there is no motion at the joint it should be okay. It's a lot faster than caulking.
Here's an illustration of the hub-and-spigot method:
Whatever method you choose, your first job is to remove the detritus of the old failed joint from the cast iron hub. Don't skimp on this -- get it all out. You'll thank yourself later.
I see that Tester101 has already illustrated a donut. Here is a picture of a PVC spigot adapter.
With the PVC spigot you use epoxy filler (e.g. SteelStick) or hydraulic cement instead of lead.